The invention relates to an improved method utilizing a submerged system for efficiently mixing gas with waste water and for flushing accumulated debris from such submerged system.
Industrial waste, sewage and the like are commonly purified by pumping the liquid into a large tank pond or basin where a bacteria population consumes the inorganic and organic material. Because the dissolved oxygen in the waste water is usually insufficient to support the required population of bacteria, the water must be aerated. This can be done with a surface aerating machine which has beaters extending into the waste water from above the water surface to agitate the water and incorporate air. Alternatively, air can be diffused through the bottom of the basin, e.g., through a porous medium. Surface aerators are not efficient and cause certain mechanical problems. The energy loss of diffusing air is also great and a diffused system is not suitable for installation in an existing pond.
Waste water can also be aerated by pumping through submerged tubes with openings through which air is drawn or pumped into the tubes to create turbulent mixing. Such devices include vortex, jet, Venturi and impingment type devices and are much more energy efficient than diffused or surface aeration systems.
One problem which can arise with systems of this sort in which water and gas are mixed in a chamber is that small particles in an aeration basin or pond can be caught within the mixing chambers, the pump or the conduits therebetween, to eventually clog the same. In sewage treatment, material such as hair, paper, cloth, etc. will become lodged in the chambers, eventually blocking water flow and reducing the effectiveness of the system. Since submerged systems of this type normally pump a great volume of water, even a small number of particles in a large basin will eventually become lodged within the mixing chambers. It is not normally desirable to shut down the system for maintenance, and removal of this material, even when the basin is drained, can be a difficult task.
However, these systems can be flushed of such debris by directly or indirectly connecting the inlets of each of the mixing chambers to which waste water is normally supplied for aeration to a higher, backflush location closer to or above water surface. If the pump is turned off while air continues to flow into the chambers, the difference in pressure between the water at the mixing chambers and the higher location causes flow of the air backward through the inlets to that back-flush location to flush the system. Surprisingly, the air pumps waste water at a substantial flow rate and pressure backward through the system. A separate line can be used with a valve to flush the debris directly above the surface where it can be collected. The waste water can be back-flushed through the pump to clean the pump screen provided that the pump and its strainer are mounted above the mixing chambers.
The air can be intermittently turned on and off to create pulsations of water which act as a hammer to dislodge debris.
Other objects and purposes of the invention will be clear from the following detailed description of the drawings.